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What are the risk factors for anal cancer?

A risk factor is anything that affects a person’s chance of getting a disease such as cancer. Several factors can affect your risk of anal cancer. But having a risk factor, or even several risk factors, does not mean that you will get cancer. And people with few or no risk factors can still get cancer.

Risk factors for anal cancer

HPV (human papilloma virus)

Most squamous cell anal cancers seem to be linked to infection with the human papilloma virus (HPV). Still, most people with HPV infections do not get anal cancer.

HPV is a group of more than 150 related viruses. Some types are more likely to cause cancer than others. HPV can also cause cancers of the cervix, vagina, and vulva in women, cancer of the penis in men, and throat cancer in both women and men.

HPV is spread from one person to another during skin-to-skin contact with an infected area of the body. HPV can be spread during sex – including vaginal, anal and oral sex. It can even be spread through hand-to-genital contact.

An HPV infection can also spread from one part of the body to another. This means that an HPV infection can start in the genitals and then spread to the anus.

Infection with HPV is common, and in most cases your body is able to clear it up on its own. But in some people the infection does not go away and becomes long lasting (chronic). Chronic infection can eventually cause certain cancers, including anal cancer.

HPV in men: For men, the 2 main factors that impact the risk of genital HPV infection are circumcision and the number of sex partners. Men who are circumcised (have had the foreskin of the penis removed) have a lower chance of getting and staying infected with HPV. The risk of being infected with HPV is also strongly linked to having many sex partners (over a man’s lifetime).

HPV in women: In women, HPV infections occur mainly at younger ages and are less common in women over 30. The reason for this is not clear. A woman’s risk is increased if she has sex at an early age and has many sexual partners. But even a woman who has had only one partner can still get infected.

Anal warts

Anal warts are caused by infection with HPV, but from types different from those most likely to cause anal cancer. Anal warts themselves are unlikely to develop into anal cancer, but people who have had anal warts are more likely to get anal cancer.

Having certain other cancers

Women who have had cancer of the cervix, vagina, or vulva are at increased risk of anal cancer. This is likely because these cancers are also caused by infection with HPV.

HIV infection

People who have the human immunodeficiency virus (HIV), the virus that causes AIDS, are much more likely to get anal cancer than those who don’t. For more on HIV and AIDS, see our document HIV Infection, AIDS, and Cancer.

Sex

Having many sex partners increases the risk of HIV and HPV infection, as well as anal cancer.

Having anal sex is a risk factor for anal cancer in both men and women, especially for those under the age of 30.

Smoking

Current smokers are several times more likely to have cancer of the anus compared with people who don’t smoke. Quitting smoking seems to reduce this risk. People who used to smoke but have quit are only slightly more likely to get anal cancer compared with people who never smoked.

Weakened immune system

People with weak immune systems are at higher risk for anal cancer. This includes people with AIDS and people who have had transplants and who must take drugs to suppress their immune systems.

Race and gender

Anal cancer is more common in women than men overall and in most racial/ethnic groups. But in African Americans it is more common in men than in women.